This invention relates to a variable incidence oblique illuminator device which is designed to be employed in optical inspection apparatus, and more particularly in apparatus of the type in which, relative to the associated optical axis, the angle of incidence of the light illuminating an object can be varied from 15° to 75°. Even more particularly this invention relates to a specially designed Fresnel lens moveable relative to the object that is being viewed to direct illumination at different angles of incidence onto the object.
Over the years a variety of apparatus have been developed for the purpose of illuminating an object which is to he inspected, for example items that are being inspected by countour projectors, optical comparitors, microscopes and other inspection systems. Typically an image of the illuminated object is then projected through a lens to an observer's eye, or more recently through video inspection apparatus. For best results, light or beams of light are directed obliquely downwardly onto an object that is being inspected better to illuminate edges or curved surfaces of an object. The oblique beams are directed at angles of incidence to the optical axis of the object that is being inspected. U S. Pat. No. 4,567,551, No. 5,897,195, No. 5,690,417 and No. 6,179,439, all of which are assigned to the same assignee as the present application, disclose a variety of different apparatus for projecting beams of light obliquely onto the surface of an object that is being inspected.
For example, U.S. Pat. No. 4,567,551, beaters from four different light sources are directed onto the reflective surfaces of four mirrors, which then reflect the light through a Fresnel lens onto the object that is to be inspected. In U.S. Pat. No. 5,897,195 a plurality of circular arrays of light emitting diodes (LEDs) surround a cylindrically shaped, Fresnel-like diffuser element which then directs the light beams from the LEDs at different angles of incidence to the optical axis of the apparatus, and onto the work that is being inspected. Variations of these multiple array LED illuminating systems are disclosed also in U.S. Pat. No. 5,690,417 and No. 6,179,439.
Although the above-noted apparatus disclose various ways of directing illumination at different angles of incidence onto an object that is being inspected, such apparatus also have the need for employing large arrays of light sources and associated Fresnel-like diffusers in order to direct onto a workpiece a large number of beams at different angles of incidence to the optical axis of the associated apparatus.
It is an object of this invention, therefore, to provide for such apparatus an improved illuminator device that employs only one circular array of light beams, and which array of beams can be directed optionally at different angles of incidence to the optical axis of the workpiece that is being inspected.
Still another object of this invention is to provide for apparatus of the type described an improved illuminator device having a circular array of light beams directed onto a Fresnel lens adjustable toward and away from art inspected object selectively to alter the angle of incidence of the light illuminating the object.
A further object of this invention is to provide for inspection apparatus an improved illuminator device of the type described which includes a Fresnel lens adjustable axially of the optical axis of the apparatus to focus light on an object and at selectively different angles of incidence to the optical axis.
Other objects of the invention will be apparent hereinafter from the specification and claims particularly when considered in conjunction with the accompanying drawings.